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== Oxygen sensors==

The Heated Oxygen Sensors (HO2S) are commonly known as O2 sensors or lambda sensors.
They are used to monitor, in real time, whether the air–fuel ratio of a combustion engine is rich or lean.
Note: the upstream 02 sensors have a dramatic effect on performance and fuel economy,
while the down stream sensors are only used to monitor the performance of the catalytic converters and emissions.

They work by producing a voltage from approximately 1.0V during rich operating conditions to 0.01V (10 mV) during lean operating conditions.
The sensor is like an open circuit and produces no voltage when it is below 360C (600F).

The powertrain control module (PCM) supplies a bias voltage of about 450 mV between
the heated oxygen sensor high signal and low signal circuits.
The HO2S varies the voltage within a range of about 1,000 mV when the exhaust is rich,
down through about 10 mV when exhaust is lean.
The PCM constantly monitors the sensors' signal during closed loop operation and compensates
for a rich or lean condition by decreasing or increasing the fuel injector pulse width as necessary.
If the HO2S voltage remains at or near the 450 mV bias for an extended period of time,
P0154 diagnostic trouble code (DTC) will be set.

Read more at: http://en.wikipedia.org/wiki/Oxygen_sensor

=== Location ===
* Left (G3/3) and right (G3/4) sensors before (or upstream) of the Catalytic Converter TWC (KAT).
* Left (G3/5) and right (G3/6) sensors after (or downstream) of the Catalytic Converter TWC (KAT).

[[File:W220_O2_Heated_Oxygen_Sensors.JPG|400px]]

=== Parts ===

[[M112]]/[[M113]]:

* A0015405117 - left/right upstream sensor. Bosch 16274/0258006274 (70 EUR)
* A0015406017 - left/right downstream sensor. Bosch 16276/0258006276 (70 EUR)

{|
|[[File:Bosch_0258006274.jpg|thumb|none|Bosch 16274 (left/right upstream sensor)]]
|[[File:Bosch_0258006276.jpg|thumb|none|Bosch 16276 (left/right downstream sensor)]]
|}

====Cable lengths====
The W220 oxygen sensors are electrically interchangeable but have different cable lengths:
* Upstream sensors have longer cable (wire length: 440mm, total length: 460mm)
* Downstream sensors have shorter cable (wre length: 322mm, total length: 340mm)

[[File:W220_Heated_Oxygen_Sensors_Front_or_Upstream_%28Long_Cable%29_Rear_or_Downstream_%28Short_Cable%29.JPG|thumb|none|Upstream vs downstream cable lengths]]

=== Issues ===
Oxygen sensors have a limited lifetime, typically 160,000 Km (100,000 miles).

Symptoms of a failing sensor include:
* Warning light on dash,
* Increased tailpipe emissions,
* Increased fuel consumption,
* Hesitation on acceleration,
* Stalling,
* Rough idling.

==== Heating element failure ====
The sensor contains a heating element which often fails by going open circuit.
The resistance of a typical W220 heater element has been measured as 9.2 Ohms.
The specified heater resistance is TBD.

Resulting Fault Codes are:
* P20BF-004 G3/3 Left HO2S before TWC (KAT) open circuit in sensor heater line (P0156)
* P2082-004 G3/3 Left HO2S before TWC (KAT) open circuit (P0154)

==== Contamination ====
Contamination of the oxygen sensor can result from the use of an inappropriate RTV or silicon sealer (not oxygen sensor safe) or excessive engine coolant or oil consumption.
* To check remove the sensor and visually inspect the portion of the sensor exposed to the exhaust stream in order to check for contamination.
* If contaminated, the portion of the sensor exposed to the exhaust stream will have a white powdery coating.
* Silicon contamination causes a high but false sensor signal voltage (rich exhaust indication). The control module will then reduce the amount of fuel delivered to the engine, causing a severe drive-ability problem.
* Eliminate the source of contamination before replacing the oxygen sensor.

=== Connector pin diagram ===
{|
|
* Pin 1 (white) - heater
* Pin 2 (white) - heater
* Pin 3 (grey) - signal low
* Pin 4 (black) - signal high
|[[File:O2_Sensor_Connector_Pin_Diagram.JPG|200px]]
|}

=== Electrical wiring diagram (upstream sensors) ===
{|
|[[File:Electrical_Wiring_Diagram_HO2S_Upstream_of_TWC_KAT.JPG|500px]]
|Sensor connector to Power Control Module (N3/10):
* Pin 1 (red or red/green) - heater ground
* Pin 2 (brown or brown/black) - heater +12V
* Pin 3 (green) - signal low
* Pin 4 (black) - signal high
|}

=== DIY ===

{|
|{{#ev:youtube|https://www.youtube.com/watch?v=4ob-ASqGp7M|320|center|Sensor location and test|frame}}
|{{#ev:youtube|https://www.youtube.com/watch?v=VaK4RGenYQA|320|center|Downstream sensor replacement|frame}}
|}

The following codes may require replacement of the O2 sensor 2:

Engine codes for Bank1 Sensor 2:
* P2031 Exhaust Gas Temperature Sensor Circuit (Bank 1 Sensor 2)
* P2032 Exhaust Gas Temperature Sensor Circuit Low (Bank 1 Sensor 2)
* P2033 Exhaust Gas Temperature Sensor Circuit High (Bank 1 Sensor 2)
* P0136 O2 Sensor Circuit Malfunction (Bank 1 Sensor 2)
* P0137 O2 Sensor Circuit Low Voltage (Bank 1 Sensor 2)
* P0138 O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)
* P0139 O2 Sensor Circuit Slow Response (Bank 1 Sensor 2)
* P0140 O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)
* P0141 O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)

Engine codes for Bank2 Sensor 2 are:
* P0156 O2 Sensor Circuit Malfunction (Bank 2 Sensor 2)
* P0157 O2 Sensor Circuit Low Voltage (Bank 2 Sensor 2)
* P0158 O2 Sensor Circuit High Voltage (Bank 2 Sensor 2)
* P0159 O2 Sensor Circuit Slow Response (Bank 2 Sensor 2)
* P0160 O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 2)
* P0161 O2 Sensor Heater Circuit Malfunction (Bank 2 Sensor 2):

===DIY Articles - Heated Oxygen Sensors (HO2S)===

* http://www.benzworld.org/forums/w203-c-class/1474361-p0154-code-wont-go-away.html
* http://www.benzworld.org/forums/w203-c-class/1474361-p0154-code-wont-go-away-2.html
* http://www.hotrodlane.cc/New%20LS%20Links%20Page/LS%20trouble%20codes/DTC%20P0154.htm

Oxygen sensors - Revision history

Pokseva: Restructured